papa tiger

I believe the HEC test shows lifetime fuel economy. Just navigate the tests. By engine braking I believe he means the trailer tow system of downshifting when slowing down, also downshifts going down steep hills with the cruise control engaged to hold set speeds.

jejeosborne

Interesting point but how do you do this in the real world? This will slow you down too quickly in most instances in my mind vs coasting which allows you time for watching the upcoming signals. Do you stay on the gas longer coming to a stop sign because you are going to let the engine braking slow you down quicker than coasting? I can see it a possible option on a stop needed at the bottom of a hill but not much anywhere else. I guess the math would be something like: coasting would be more time at idle which is using gas vs engine braking is more time at cruise throttle because you're stopping time is less.

After doing some research I have found that this is only popular when going down a pretty steep long hill. I try to coast at idle and not bleed off any of my stored energy until necessary. Engine braking is going to bleed off this stored energy. I guess that once you see a stop is imminent, downshifting manually may save a minute amount of fuel. The transmission engineers designed these to coast and not engine brake for a reason.....to save fuel. Vastly mistaken I think maybe not.

gouldje

When i said back to where it was, it is the surging at between 45-55 mph in 6th gear situations. Also have noticed a lot of soot on the pipe lately.

RickyCRX

First of all, let's define a few terms for argument sake...

a) "Coasting" is putting the transmission in Neutral and leaving the engine at idle while free-wheeling along.
b) Engine braking is when the transmission is engaged and/or torque convertor is locked-up and your engine speed is *anything* ABOVE an idle speed, with the throttle position at 0% (foot completely off the gas pedal).

The F150 does *not* "coast" (free wheel) when you simply take your foot off the gas pedal. If it did, you would immediately notice the tach drop a few hundred RPM or more (or it would return completely to idle) as soon as you take your foot off the gas at highway speeds, and it does not. The truck will keep downshifting through the gears as you slow down, keeping the transmission engaged, even with your foot completely off the throttle.

Now, ANY time your throttle position is 0% and the engine speed is above "idle" (which is roughly around 600rpm or so, with transmission in neutral), the vehicle is "engine braking" and helping you slow down without the use of friction brakes. During this particular condition, *no* fuel is being injected into the cylinders at all, which is why your instant MPG bar will 'peg' itself at the highest level, and if you were to zero it out in this condition, it will immediately show you 99.9mpg, because you are basically getting 'infinite' mileage per the computer at that point in time (you have moved a given distance with no fuel burned at all, so it doesn't know how to compute that value, so it simply reads out the highest value that it is programmed to give).

So no, I do not keep giving it throttle if I see people up ahead stopping. I simply let off the gas and let the truck engine brake down. In 6th gear, it will hold until you get down to 40mph... In 5th gear it will hold until you get down to 30mph, then 4th will hold to ~20mph or so, etc... It will downshift through the gears for you, engine braking the entire way until you are down to quite a slow speed.

jejeosborne

Let's redefine those terms.

Coasting is when the engine is not supplying or absorbing energy to/from the drivetrain. Engine braking is when the engine is absorbing energy from the drivetrain. Obviously there is the third element of acceleration which means the engine supplies energy to the drivetrain. RPM doesn't matter in this equation. Yes if I let off my gas at speeds under highway speed, my rpm stays the same but the engine is not braking or absorbing energy unless I force a downshift. It is basically disengaged. In fact, if I slide the shifter to neutral, my rpms increase on my 2011 ecoboost when moving.

When I am in tow haul mode, engine braking will happen as the engine will slow the truck down. Also, engine braking CAN take place at idle speed. You said it yourself, if no gas is injected, how else would the engine be turning. Basically, RPM is not a factor. In your example you were coasting a majority of the time or else your tach would be bouncing up at each downshift. Wind drag is what is slowing you down.

In general, engine braking is a detriment to fuel mileage since it is bleeding off stored energy you had built up. Yes there are those few instances that engine braking can save fuel such as steep hill descents or quick stops where there isn't enough room to coast.

http://en.m.wikipedia.org/wiki/Engine_braking

RickyCRX

At least we agree on this... "Coasting" is what you define as "NEUTRAL" on the transmission.

This is where you are incorrect -- because of the way the ECU is programmed, it will CUT FUEL FLOW TO THE ENGINE if it is above idle speed while the transmission is engaged and the throttle position is at 0%. If you don't believe me, go get a scan gauge and look at the injector flow and/or O2 sensor readings for yourself. Stop arguing this point.

Really? Then why does the truck slow down more quickly in this condition as opposed to simply putting the shifter in NEUTRAL? Because it is *engine braking*

No, the transmission is NOT disengaged just because you took your foot off the throttle.

That is only a matter of ECU programming. For some reason, Ford has that programmed into their ECUs and has been that way on most of their vehicles for many years. I am guessing they do this so that when you do put it back in gear, there is not an abrupt 'slow down' due to the engine having to quickly get back up to the vehicle speed.

You don't have to be in tow/haul for the engine to help brake the truck. Tow/haul simply allows you to downshift the truck one gear at a time by using the brake pedal to signal the ECU to downshift, rather than having to shift on the shifter. That's all it is doing.

You are incorrect, once again. If the engine has slowed all the way down to IDLE speed, then the ECU is once again injecting fuel into the engine, and you are no longer 'engine braking.' The engine is now powering the vehicle to roll at a slow creep/roll. The truck is no longer slowing down, it is maintaining speed, therefore it is no longer BRAKING, is it?

Obviously you don't pay attention to your gauges closely enough, because the tach DOES 'bounce up' at each downshift. Every time the truck gets down to around 950-1000rpm without your foot on the gas pedal, the tach will then jump back up to 1100-1200 as it drops down to the next lower gear because.... drum roll.... it is *engine braking* Pay closer attention next time you drive and you'll see it.

Wind resistance is one component of what's slowing you down, but it is not the only component. There is friction from the rotating components in the driveline, friction from the tires, the vacuum created from the closed throttle plate, giving you your engine braking, etc.

You are incorrect, once again, about it being detrimental to fuel economy. In a perfect world, you only 'burn' (foot on gas pedal) long enough to where you can 'engine brake' (zero burn) to the next stop such that you don't have to touch the friction brakes...ever. This would net you the absolute best fuel economy. Obviously, we don't live in a perfect world, but the concept is still the same. If you can leave the truck in gear and engine brake as far as possible so you have to use the brakes as little as possible, this will net you the absolute best fuel economy.

Yay, somebody knows how to use Google -- now go back and re-read that article under the 'petrol' section, then the "applications" section. You are arguing *against* the very article you just linked here. You wouldn't be arguing this point if you understood how the mechanics and electronics of a vehicle actually worked.

Do yourself a favor and get a scan gauge that will show the real-time readings of sensors. I have done ECU programming and studied the inputs from many various sensors on vehicles in the past when I have tuned my own turbo and supercharged vehicles that didn't come that way from the factory.

RickyCRX

The surging is really disappointing to hear that it's back after the re-tune. I really want to find a way to get rid of that under low rpm/high load conditions. Ford, are you listening?

jejeosborne

This is all coming down to what you and I consider engine braking.

What do you call it when engine speed matches the current speed of gear ratio in the driveline? Example, peddling a bicycle in a gear where there is no tension on the chain. Basically matching the wheel speed and crank speed but not absorbing or adding power to the wheel.

This is BASICALLY what the automatic transmissions does to improve your coasting ability. I consider and so do most, that engine braking is an aggressive difference in ratios in which the engine revs to much higher than normal level by downshifting earlier than necessary. In tow/haul mode the transmission will do this to help slow the load down saving your brakes. In normal mode the exact opposite happens if I let my foot off the gas. If not in the highest gear, it up shifts to a higher gear making the engine braking effect less. I agree that there is a very slight "engine braking" taking place but consider this more coasting than braking thus our differences in the term. Hypermilers generally consider engine braking bad because it is still considered braking. They only consider it good if a stop is imminent (for the reasons you describe) but they don't want to bleed off momentum if there is no need to stop or slow down.

jcain

I like to ride my biiiiiicycle....

RickyCRX

In the case of the F150, there is no condition in which you can replicate that exact scenario, unless you shift the transmission to Neutral.

No, it isn't. https://www.fleet.ford.com/showroom/...ng%20Guide.pdf

Go to page three. At the bottom right corner of the page, in blue text... What does it say? "All engines include Aggressive Deceleration Fuel Shut-off (ADFSO) to help maximize fuel economy."

This means that even Ford says (in their own fancy lingo) the exact same thing I am saying. When you are decelerating (foot off the throttle), the ECU cuts off fuel flow. No matter what you THINK the terms mean -- with a closed throttle plate, the transmission engaged, engine speed above idle and the ECU not injecting fuel, YOU ARE ENGINE BRAKING. I said in one of my earlier posts that the engine doesn't have to be at high revs to be engine braking. You can see and feel engine braking at 1100rpm in these trucks, at lower speeds.

That is an extreme mode of engine braking, when you downshift multiple gears to get the revs up to save brakes on big downhills with big loads.


...but it is still there.

This is not 'coasting...' It is, in fact, still engine braking.

Coasting is, as you said before, NO energy being added or removed by the engine... Also known as *neutral*.

Of course! Why would I want to do more extreme engine braking than what the ECU does in 'normal mode' unless I need to stop? And even then, the only reason to do that is to save brakes. The F150 burns zero fuel as you are decelerating to a stoplight, with foot completely off throttle. This is the point I was trying to drive home to people in my very first post in this thread. The more time you spend *ON* throttle roaring up to a red light/stop sign, the worse your fuel economy will be. The longer distance you can spend at 0% throttle and engine braking (hopefully you now understand the proper terminology better, after this discussion), even if it is minimally in the highest gear possible, this will net you the best economy.

I watch people all the time driving like idiots around me -- there's a red light 800' down the road, I'm engine braking in 6th gear at 45-50mph, and they move over a lane and gas it, pass me, then stand on the brakes and stop at the light. About 3-4 seconds later, I gently roll up next to them, having burned no fuel until just a couple seconds before the truck actually came to a stop. They did nothing but burn extra fuel and use extra brake material just to get to the same spot at the same time.

This is why I tend to heavily discount claims of "Woah is meeee.... My truck only gets 13mpg, without towing a trailer...." Sure, there may be a few trucks out there that have some faulty sensors or something wrong with them and are legitimately getting horrible mileage, but with how much mileage changes because of wind speed and direction, and driving style, I think most folks would net FAR better economy just by taking a close look at their driving style and driving conditions and taking that into account.